Itamar Ferreira

Propriedades mecânicas e de corrosão de dois aços inoxidáveis austeníticos utilizados na fabricação de implantes ortopédicos

ASTM F 138 austenitic stainless steel is extensively used as an orthopedic implant material. However, some aspects, such as low strength in the annealed condition and susceptibility to localized corrosion, limit wider use of this kind of steel. Recently, a high-nitrogen austenitic stainless steel, specified in the standard ISO 5832-9, has been indicated as an alternative to ASTM F 138 steel for more severe loading and permanent application inside the human body. In this work, microstructure, mechanical properties, corrosion resistance and fatigue behavior of both steels were determined and compared. ISO 5832-9 steel displayed better mechanical and corrosion behaviors than did ASTM F 138 steel. The combination of these features lead ISO steel to enhanced fatigue performance in both neutral and aggressive environments. Analyzed were the role of nitrogen in solid solution, combined with niobium in the Z-phase, and the factors that led to superior ISO 5832-9 properties.

Sinterização de uma mistura de cavaco de aço inoxidável com pó do mesmo material: uma nova tecnologia para a reciclagem de metais?

The reuse of materials has as its main objective to minimize environmental impacts and to rationalize the use of energy chains. In the present work, samples of scraps of 316 stainless steel mixed with powder of the same material were sintered. For this case, the percentage of scrap was varied from zero to 25% in weight, with 5% increases. After compacting, under a pressure of 600MPa, the samples were sintered simultaneously at a temperature of 1473 K. The mechanical behavior of the final product was evaluated through Assays of Transversal Rupture recommended and normalized by the MPIF - Metal Powder Industries Federation. Using Conventional Quantitative Metallography, the analyses of the sintered samples demonstrated regions of intense diffusion, therefore, regions of sufficiently intense sintering. The mechanical resistance of the samples was compared with the mechanical resistance of the sintered stainless steel with no scrap. The results were greater than expected, demonstrating the viability of this new procedure.

Effect of Heat Treatments on Mechanical Properties and Fatigue Resistance of Ti-35Nb Alloy Used as Biomaterial

Titanium alloys form the most versatile class of metallic materials used as biomaterials. Among them it is foreseen that the  type titanium alloy will be a prominent one for orthopedic applications. Aim of the present work was to prepare and characterize a  type titanium alloy containing 35 wt.% Nb. Samples were cooled from the  phase temperatures at different rates. This work includes the effects of heat treatment on the microstructure and hardness, tensile and fatigue properties in air at room temperature. The results showed that microstructure of slow cooled samples are formed by precipitates of  and  phases in a  matrix. After rapid cooling, the microstructure consists of  phase and ” martensite. Mechanical testing showed that the elastic modulus and Vickers hardness of slow cooled samples were significantly higher than that obtained by rapid cooling. On the other hand, it was observed that slow cooled samples showed higher tensile strength and lower ductility. The rapid cooled sample showed fatigue resistance higher than that of slow cooled samples.

Case study of an evaluation of a Stacker Boom Luffing Pulley by Irwin's model and under BS 7910 guidance

A case study on evaluation of a heavy–duty Stacker Boom Luffing Pulley was presented. Irwins fracture toughness method and the British Standard were used to help in the decision–making process. Using inspection, discontinuities were found at the first look in the cylinder cross–section at the region of welding of the cylinder ends. A more detailed analysis was conducted by ultrasonic mapping, crossing the cylinder transverse thickness and longitudinal to its length. The final decision took into account accurate analysis of the stress σ1 (Principal Stress) from Finite Element Method (FEM) and σref based on British Standard, and comparing the defect real size and the critical crack size calculated by Irwin equation.

Temper Embrittlement Analyses at HAZ in New Generation of 2-1/4Cr-1Mo Steels by CTOD Tests

Temper embrittlement susceptibility was analyzed at HAZ of welded joints at room temperature in new generation of 2-1/4Cr-1Mo steels. Assessment was made by fracture toughness parameter CTODm in welded joints at coarse-grain heat affected zone (CGHAZ) and fine-grain heat affected zone (FGHAZ). Microstructural analysis was made before and after CTODm tests to place correctly fatigue pre crack at CGHAZ or at FGHAZ. Temper embrittlement simulation was made by “Step Cooling” treatment. Hardness results and microstructural analysis proved the use of stress associated with “Step Cooling” made the efficacy of this treatment better. The control of impurities content in the steel avoids development of temper embrittlement. This was confirmed by fracture toughness experiments at room temperature. No significant variation on CTODm results of three different situations of treatment and between CGHAZ and FGHAZ were observed. Scanning Electron Microscope analysis indicated fracture mechanism after embrittlement simulation was microvoids coalescence.Copyright

Failure Analysis of a Set of Flapper Valves Under ALT With Alternative Test Device

In search of further understanding and continuous improvement of mechanical products which suffer dynamics loading, several methods of analysis have been applied, among them, computational simulations and laboratorial experiments. This paper aims to describe the fail- ure mechanics of a regular flapper valve and valve reed used on Hermetic Compressors when tested under accelerated test conditions by a special device, created for testing purpose. The results obtained from the valve reed were plotted on a graph, which reveals the endurance under fatigue, versus the device speed/load change. These curves represent the obtained valve reed lifetime by Weibull ALT (accelerated life test) (statistical anal- ysis). The values obtained were analysed using the normality and the probability approaches beyond t-student. The Weibull ALT graph (fatigue lifetime), microscopic analysis by SEM (scanning electron microscope) and EDS (energy dispersive spectroscopy) were performed on the failed valve reed surface as well as on the valve plate seat utilised throughout the tests.

Uma Metodologia para a avaliação dos gradientes de tenacidade à fratura ao longo da camada cementada do aço SAE 5115

Este trabalho propoe um modelo para avaliar pontualmente as variacoes de tenacidade a fratura ao longo da camada cementada de um aco SAE 5115. A pequena espessura dessas camadas impede a retirada de corpos de prova nas dimensoes especificadas pelas normas de ensaios de tenacidade a fratura. Assim, para simular uma camada cementada retirou-se corpos de prova de tracao e de tenacidade a fratura de amostras de acos SAE 5115, 5140, 5160 e 52100 assumindo a influencia local apenas da variacao do teor de carbono e considerando que os teores dos demais elementos de liga sao essencialmente constantes. Os corpos de prova apos eletrodeposicao de cobre foram tratados termicamente numa carga industrial de cementacao, tempera e revenimento para serem submetidos aos efeitos termicos sem absorcao de carbono. Os resultados da analise microestrutural, dos ensaios de microdureza, de tracao e de tenacidade a fratura foram agrupados em um unico grafico e comparados com o perfil de cementacao de pecas de aco SAE 5115 tratadas nas mesmas condicoes. Foi confirmado que a tenacidade a fratura varia inversamente proporcional a microdureza (HV1) e que a previsao do comportamento de uma trinca numa camada cementada pode ser feita por meio de equacao ou diagrama que relacionam a miicrodureza HV1 com a tenacidade a fratura (K1c ou CTODc) Abstract

Fracture Toughness of the API 5L X65 Steel Submitted to Intercritical Heat Treatments

The intercritical heat treatment effect on the mechanical properties of the API 5L X65 steel, microalloyed with Ti and Nb, widely used in welded structures, was investigated. The embrittlement, observed by several authors in the intercritical region of the heat affected zone of welds performed in HSLA steels, is closely related to the volume fraction of M-A constituent, formed in the cooling. Just upon the homogenization and normalizing heat treatments, the specimens were submitted to different intercritical heat treatments, performed at 780 °C for 30 minutes and cooled with various Δt8/5 rates, with the purpose of varying the microstructure. High fracture toughness was obtained with the lower cooling rate. Also, it was verified that the low M-A constituent volume fraction was not enough to promote reduction on the fracture toughness.Copyright